master 61a5bbc683: Really fix extended frame synchronization

[Po Lu]

branch: master
commit 61a5bbc6836337479f5d8dba1897380b1c63bc25
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Really fix extended frame synchronization
    
    * src/xterm.c (XTframe_up_to_date): Make sure the extended
    counter ends up even.
---
 src/xterm.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/xterm.c b/src/xterm.c
index d3d8dc468c..49fc2b1bb7 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -1848,6 +1848,12 @@ x_update_end (struct frame *f)
 static void
 XTframe_up_to_date (struct frame *f)
 {
+#ifdef HAVE_XSYNC
+  XSyncValue add;
+  XSyncValue current;
+  Bool overflow_p;
+#endif
+
   eassert (FRAME_X_P (f));
   block_input ();
   FRAME_MOUSE_UPDATE (f);
@@ -1867,12 +1873,15 @@ XTframe_up_to_date (struct frame *f)
   if (FRAME_X_OUTPUT (f)->ext_sync_end_pending_p
       && FRAME_X_EXTENDED_COUNTER (f) != None)
     {
-      XSyncValue add;
-      Bool overflow_p;
+      current = FRAME_X_OUTPUT (f)->current_extended_counter_value;
+
+      if (XSyncValueLow32 (current) % 2)
+       XSyncIntToValue (&add, 1);
+      else
+       XSyncIntToValue (&add, 2);
 
-      XSyncIntToValue (&add, 1);
       XSyncValueAdd (&FRAME_X_OUTPUT (f)->current_extended_counter_value,
-                    add, add, &overflow_p);
+                    current, add, &overflow_p);
 
       if (overflow_p)
        emacs_abort ();